One known multiprocessor system configuration has a master processor which handles system level functions, such as those requiring communications with input/output devices or access to bulk storage devices such as disks and tapes, while other processing elements perform other computational functions and return an assigned job to the master processor when such a system level function is encountered. In some software systems approximately half of the execution time is spent on such system level functions. It might be assumed, therefore, that in such a system a two processor master/slave arrangement would have nearly twice the processing power as its one processor counterpart. Under certain circumstances, however, the addition of a slave processor may increase the total processing power by much less than 100 percent, sometimes less than 50 percent. One reason for this is the under utilization of the slave processors. The processing of a user transaction by a multiple processor system typically involves the selection by the master processor of program instructions and data necessary to carry out the assigned work This is referred to as the creation of a process. The master may transfer the created process to a slave processor for execution. The slave processor executes the process until a system level function is encountered which the slave processor cannot handle, and transfers the process back to the master. The master may execute the appropriate system level function and transfer the process back to the slave for further execution. The amount of time used in what is sometimes referred to as context switching, i.e. the transferring of processes between processors and performing related start up activities, may reduce substantially the time available for process execution. This is especially true for jobs requiring frequent master processor interaction.
Thus, a problem of the prior art is making efficient and cost effective use of the processing power of the equipment in a multiprocessor system. In one prior art arrangement, the master processor communicates with multiple slave processors via separate queues and load balancing is accomplished by placing new tasks on the shortest queue. However, this does not eliminate the bottleneck resulting from frequent context switching.
In other prior art multiprocessor arrangements, there are the equivalent of two or more masters each having a specifically assigned task such as communicating with certain types of input/output devices in order to avoid bottlenecks and to increase processor utilization. Such a system has inherent complexities, however in that each of the several processors must have input/output capability, thereby diminishing the advantages of a master-slave multiprocessor system.